In order to transmit audio information only to a specific subject, a directional loudspeaker has conventionally been used. In the directional loudspeaker, an audible sound signal as audio information that is modulated with a carrier wave in the ultrasonic wave band is input to a piezoelectric element, and thereby a diaphragm provided with the piezoelectric element is vibrated and a sound wave is generated. A structural sectional view of this directional loudspeaker is shown in FIG. 12.
Piezoelectric element 105 as a vibration source adheres to diaphragm 103 of directional loudspeaker 101. Diaphragm 103 is bonded, using insulating adhesive agent 111, to the tips of electrodes 109 that are fixed to base 107. Further, piezoelectric element 105 is connected to each of electrodes 109 via respective lead wire 113. In order to increase the sound pressure from directional loudspeaker 101, directional loudspeaker 101 may include resonator 115 (see Patent Literature 1, for example).
With such a configuration, a signal obtained by modulating an audible sound signal with a carrier wave in the ultrasonic wave band is input from an external electrical circuit (not shown) to piezoelectric element 105 via electrodes 109 and lead wires 113. Thereby, piezoelectric element 105 and diaphragm 103 are vibrated, and audio information is transmitted only to a specific subject, i.e. the user of the electronic device, for example.